1. Field of the Invention
This invention relates to a device for filtering a liquid containing various impurities, and particularly for filtering aircraft engine fuel.
2. Description of the Prior Art
Filters using a rotating drum are already known for such applications.
French Pat. No. 1,543,530 describes a device for filtering a liquid, comprising a filter in the shape of a bell with a perforated lateral wall, driven in slow rotation about its vertical axis, preferably by an hydraulic motor supplied with purified liquid delivered by a pump. The liquid to be filtered enters the rotating bell through the perforations in its lateral wall and, after filtration, is evacuated in an essentially axial direction through the open base of the bell. A vertical distributor is provided to atomize a fraction of the purified liquid supplied by the pump onto a vertical element on the inner surface of the lateral wall of the bell in such a way as to send the impurities deposited on the outer surface of the filter into the mass of contaminated liquid surrounding it. The operation of this filtering device is necessarily relatively unsatisfactory, to the extent that the impurities caught in the filter are sent back into the contaminated liquid, increasing its impurity content, before this contaminated liquid, enriched with additional impurities, passes through the filter. The efficiency of the known filtering device is therefore completely dubious, and in any event it requires frequent cleanings.
French Pat. No. 1,528,213 describes a device for filtering liquids containing various impurities. This device comprises a nozzle which sprays the liquid to be filtered into a fan shape from the bottom upward and against the lateral filtering wall of a drum rotating about its horizontal axis. The filtered liquid is evacuated in an axial direction through one of the bases of the rotating drum. Various elements for cleaning the drum's lateral filtering surface are provided. The cleaning may notably be accomplished by causing a portion of the liquid in the drum to flow back through the lateral filtering wall by means of a low pressure zone created outside the drum by an appropriate efflux joint extending over the entire length of the drum. This arrangement prevents impurities detached from the lateral surface of the drum from being remixed with the liquid to be filtered. However, in the mode of operation of this known device, according to which the filtering drum is driven in continuous rotation, the abovementioned efflux joint covers only a very small and probably insufficient angular width of the lateral wall of the drum. Since the mode of operation of this known filtering device provides for the drum to rotate only at regular intervals and for cleaning phases--during which the filtering operation is suspended--this arrangement is generally not applicable for filtering the fuel supplying an aircraft engine, in that it would entail interruptions in the delivery of fuel which, while brief enough, would increase in frequency depending on the level of impurities in the fuel and which would, at the very least, make ground maintenance requirements more burdensome.